Method of and apparatus for detecting and observing objects in the dark



METHOD OF AND APPARATUS FOR DETECTING AND OBSER S. 0. HOFFMAN.

VING OBJECTS IN THE DARK.

APPLICATION FILED APR. 8. I919.

Patented June 15, 1920.

4 SHEETS-SHEET IN VEN TOR AS ffoigman BY fie ATTORNEYS S. 0. HOFFMAN. METHOD OF AND APPARATUS FOR DETECTING AND OBSERVING OBJECTS IN THE DARK- APPLICATION mu) APR. B. 19:9.

1,343,393. Patented June 15, 1920.

4 SHEETS-SHEET 2.

WITNESS INVENTOR AS: O-HWMQ?! A TTORNEYS I S. O. HOFFMAN. METHOD OF AND APPARATUS FOR DETECTING AND OBSEHVING OBJECTS IN THE DARK. APPLICATION FILED APR. 8. 1919 1,343,393, PatentedJune 15, 1920.

4 SHEETS-SHEET a.

WITNESS IN VEN TOR 4 ATTORNEYS s. 0. HOFFMAN.

METHOD OF AND APPARATUS FOR DETECTING AND OBSERVING OBJECTS IN THE DARK.

APPLICATION FILED APR. 8, I919.

1,343,393. Patented June 15, 1920.

4 SHEETS-SHEET 4.

315 J/ v g 5/ .52 I

54- V z-aacll/afi M/ m im- 'SEEEEZEEFE 7 a: it: /z\ Eli-,2 1 mm I if 6 WITNESS 0 IN V EN TOR 7 By W M @J A TTORNE YS mnrnon 5 cisco,

,um'rao sum 0. HOFFMAN,

O! m APYARATUS FOR DETECTING a DAB!- PATENT OFFICE.

OI SAIN IB-ANOISOO, CALIFORNIA, ASSIGNOB 0F ONE-THIRD IO EB! ABE-LES, OF SAN FBANOISCO,

CALIFORNIA.

m OBSEBVING OBJECTS IN THE To all whom e't may concern.-

Be it known t at I SAMUEL 0. Hors- MAN a citizen of the nited States, and a resi ent of the city and county of San Fran- State of California have invented a certain new and useful Method of and AE- jparatus for Detecting and Observing O ects in the Dark, ,of which the following is a s ification.

, he invention relates to a an. apparatus for detectin and observing objects in the dark, and or detecting the resence of invisible objects by day.

The invention has for its method of and tion and observation of ob'ects in the dark I airplanes, icebergs,

higher or lower 0 he amount of this radiation emitted etection and obany object of a than itsbacksuch --as men, guns, ship funnels,

' etc. and in addition on cloudless ni hts, the detection and observation ofobjects of the same temperature as ai their background, but of a different radiation emission power, that is, objects of a and renders possible the servation in the dark of temperature ground,

.' to different color than their background. My

. device makes use of the long wave-l infra red radiation which is emitted in varying quantitylby all bodies at ordinary temeraturesin t e darkas well as in the liglgt. varidus bodies depends chiefly on their tem perature and to a less extent on their radia- -tion emission power or colors.

in this specification,

Hereafter this long wave-length at temperature radiation will be referred to as oing, will to ollowing description where fication. In said thermal radiation.

The invention possesses other advantageous features, some of which, with the forebe set forth at length in the I shall outline in full, thatparticular form of the apparatus of my invention which I have selected for illustration in the drawings accompanying and forming art of the present specirawings I have shown one s ecific form of the apparatus of my invention, but it is to be understood that I do not limit myself to such form, since the invention, as expressed in the claims, may be embodied in a plurality offorms.

drawings view of the apparatus Specification of Letters Patent.

object the detecthe apparatus shown in Patented June 15, 1920.

one form of detecting circuit used in conjunction with my apparatus. Fig. 3 is a erspective view of the thermopile mount, t e cover being removed to disclose the interior.

Fig. 4 is a cross section of the assembled mount with the thermo ile therein. Fig. 5 is a greatly on arged plan view of one type of thermopile. t

Fig. 6 is a greatly enlarged plan view of a modified type of thermopile.

Fi 7 is an elevation of one form of circuit interrupter for use with my apparatus.

Fig. 8 is a section through the interrupter on the line 8-8 of Fig. 7.

Fi 9 is a side elevation of a thermal expansion unit.

' Fig. 10 is a plan view of the thermal expansion unit.

Fig. 11 is a diagrammatic re resentation of one form of apparatus for 0 serving the image formed on a plurality of thermocouples.

Big. 12 is a diagrammatic representation of, an optical system used Fin connection with ig. 11. L

Fig. 13 is a diagrammatic representation of one form of apparatus for observing the expansion of thermal expansion units.

In accordance with m invention I concentrate the thermal radiation from a body or form an image of the body in dark radiation on a thermo-sensitive surface, such as a thermopile or group of thermal expansion units and translate the effect of such radiation or image into some physical manifestation that is capable of being observed or notfid by one of the senses, preferably by si t.

One form of the apparatus of my invention comprises a suitable casing 2 within which is arranged a parabolic mirror 3. The casing is provided with horizontal shafts 4, journaled in the yoke 5, which is mounted upon a suitable base 6 in such manner that it ma be readily oriented, as by the hand whee 7. The shafts 4 are also suitably connected to a hand wheel 8 so that the casing may be moved in a vertical arc. Secured to-the casing by the arms 9, and disposed in front of the mirror 3 is a head 12, in which is secured the mount 13 of the thermopile 14. The head is so positioned, that when the mount is secured thereto, the thermopile lies at the focus of the mirror, so that an image in dark radiation of the object at which the mirror ,is sighted, is formed on the thermopile. The head is provided with a socket, into which a projection on the mount extends and in which the extension is clamped by suitable means.

The avera e wave length of thethermal radiation uti ized in the method of my invention is about ten times the average wave length of ii ht and obeys the laws of reflection and re raction that apply to visible radiation. The absorbing power of most transparent substances for this thermal ra- 'ation is so great that the use of transparent substances is recluded, except in very thin plates and t erefore I prefer to use a mirror rather than a lens for concentrating the radiation or for forming an image of the object on the thermopile or other temperature sensitive surface.

The mount 13 is of ru ged metallic construction and is providef with a cavity in which the thermopile is disposed. The cavity is closed by a cover plate15, which is clamped thereto by suitable means such as the clamp screws 16, so that the thermopile chamber is air tight. The cover 18 provided centrally with a slot which is covered by a rock-salt plate 17, Which is transparent to these radiations. This revents all air and drafts from reaching t e thermopile. The rock-salt plate is protected from the action of moisture by a very thin coat of asphaltum varnish. The mount is also provided with a thermopile ejection plunger 20 which extends into the removable stem or projection 10. Secured to the metallic portion of the mount are blocks of insulation 11 in which the electric terminals are arran ed.

The thermopile of my invention comprises a base 18, preferably made of ivory, upon which are arranged a plurality of bismuthsilver thermocouples. The base 18 is provided with an aperture and fixed therein ver wire 21 bein on both sides of the aperture are rows of pegs 19, preferably formed of copper. The thermocouples consist of complete strands or len hs of bismuth wire and silver wire welde together at their juncture and having a very small piece of silver foil welded to the juncture. elded to a peg 19 on one side is a short piece of silver wire 21 less than 2 mm. in len h and welded to that is a short length of ismuth wire 22, the silused because a bismuthcopper weld is brittle and will not withstand vibration. Welded to the bismuth wire at its end, is a iece of silver wire 50 whichat its other en is welded to the copper post on the other side of the arture. To this second cop er st is weld dd the silver end 21 of anot er ismuth-silver thermocouple provided at its center with a piece of silver foil 23. This construction is repeated a plurality of times, producin a series of pieces of si ver foil arranged in Tine, but each se arated from and air insulated from the ad acent pieces of foil. This produces a rality of sensitive thermocouples connected together in series. The wires of each thermocouple are of such length that they sag slightly thereby providing for variations in len h due to temperature chan as.

or quick acting thermopi es, the bismuthhwire is preferably 0.07 mm. in diameter t e and the silver foil one-half mm. s uare' and 0.02 mm. thick. The pile reaches its steady temperature in less thanone second. The ends of the thermopile are connected to the metallic preferably copper posts 24-25 which extend from the ass 18 and which are insertible into the sockets 26-27 in the mount. A clamp bar 28 provided with a screw portion 31 which is provided with a thumb nut 29 is arranged at each side of the mount for clamping the posts in position. The screw 31 also acts as a binding post for connecting the lead wires to the mount, the screwing of the nuts serving both to clamp the osts and the lead wires.

e current generated. in the thermopile by the action of the thermal radiation thereon may be detected with'a galvanometer, which is preferably of the ordinary high sensitivity, low resistance, movin e011 type, having a period of one second. 'fimis type of instrument i advantageou for use when a portable instrument; trenches and in other military operations. In actual use on directing the mirror toward a sus ected spot, the background will as a rule e of diflerent temperature than the receiving surface of the thermopile and this will result in a permanent galvanometer deflection. A potentiometer compensating arrangement is therefore used whereby an adjustable small current from a battery 32 can be sent through the galvanometer opposing the current from the thermopile and thus eegiing the galvanometer s t at the center 0 the scale independent 0 the temperature of the back and. When portability'of the silver wire 0.025 mm. in diameter instrument is not.

is desired for use in y required, such as in installation on ship-' board, the galvanometer maybe disper ggd with and the direct current from the theme pile converted into a ulsating current, which may be readily amp ified in a vacuum tube or electron relay. is then passed through telep one receivers, producing audible reception. Considerable care is necessary in the selection of the device or chopper for converting'the direct current intoa pulsating current, so that induction and stray thermo-electric efl'ects are avoided. In Figs. 7 and 8 I have shown a suitable formof chopper which consists The amplified current essentially of an extremely lightsuspended under observation is suiiicient, a number of system, tuned to vibrate at the frequency of independent thermopiles distributed over highest audibility. 'The chopper shown the receivi surface in the focus. of the comprises a casing 33 having suspended mirror may employed. Each thermopile therein a stretched wire 34 to which is seor thermocou le 51 is separately connected 7o cured. a copper vane 35 which is causedto to a fine meta lic strin 5 mounted between vibrate by minute streams of air issuing the poles of a power ul electro-ma et 53. from the nozzles 36. Secured to the wire The plurality o strings are arrange in parbelow and spaced from the vane, so that its allel relation. between the poles and a curmotion will be less than that of the vane, rent or a variation in current in any strin is a contact piece 40, preferably of copper, causesa very slight transverse movement 0 which is moved by the oscillating vane, to the string, each string being affected by make contact alternately with the two com the amount of energy 'present at the spot tacts 37-38, preferably of copper, connected of the corres onding thermopile in the radito one wire of the circuit. e other wire ant image. e pole pieces of the electroof the circuit is connected to the adjusting magnet 53 are provided with slots 54 screw 39. Care must be exercised to have through which the strings may be observed. no dissimilar metals in contact in the circuit The movement of the strings is so slight that to generate stray thermo-electric currents it can be observed only with a microscope and to have no rubbing contacts or rapidly and on account of the large number of a moving dielectrics. It is advantageous also strings, direct vision in this manner becomes to insert a small transformer between the T impractical, if not impossible. Inorder to am lifier and the interrupter 30. permit the movement of the strings to be he thermopile shown in Fig. 5 is useful observed, I have employed the optical syswhere the instrument is to be traversed in tem shown in Fig. 12. A beam of light is one plane only, uch as for locating raiding directed through the slots 54 and the lens parties from'the trenches and for other pur 55, forming an image of the strings on the poses, but when the instrument is to be travmirror 56. The mirror 56 oscillates, brin ersed in two planes, that is, the vertical and ing the image of each string successive y the horizontal, for detectin and locating into the focus of the microscope 57 Them; airplanes or other objects in the air, the microscope projects an enlarged image of form of thermopile shown in Fig. 6 is adthe strings on the mirror 58 which is convanta ous. In this arrangement, two sepanested to and oscillates in time with the mirrate t ermopiles are employed, the receiving ror 56 and from the mirror 58, the images surfaces bein preferab y disposed at right are reflected on a screen 59. Since both -mirangles to eac other. The s lver foil surrors oscillate in synchronism and to the faces are all air insulated from each other same degree, the image of a string on the and the two thermopiles are insulatedirom screen will move only when a string moves each other. Each thermopile is connected and no movement of an image is efiected by to a se arate galvanometer and when defiecthe movement of the mirrors. The screen tion 0 both galvanometers is obtained it is is preferably rovided on its surface with evidence of the formation of the ima e at contiguous ig t and dark lines and the the intersection of the thermopiles, in icatimages of the strings normally fall on the ing that the axis of the mirror is on the li ht lines, making such portion dark. obf'ect sought. The opening in the thermohen a string moves, the image m oves onto pi e mount is shaped to corres ond to the a dark portion of the screen, exposing the I shape of the thermopile so thatt e radiation white line, thereby accentuatmg the visimay reach both surfaces. Scales are probility of the movement of the strings. vided on the mirror mount so that the exact When detail is required, a large number of direction of the ob'ect may be read. radiation sensitive units must be used and The ap aratus heretofore described will very compact units must be chosen. I may detect an locate an object, but will not prouse the radiometer, the radiomicrometer or a duce an image thereof. When it is desirable simple expansion unit. The radiometer and to obtain a more or less clearly defined image radiomicrometer are the same, except for of the object, I use what I have termed an their minute dimensions, as the wellown electro-mechanical retina to translate the laboratory instruments. One form of therenergy image produced by the concave mi'rmal expansion unit is shown'more or less ror, into a'luminous image. To be of-value diagrammatically in Figs. 9 and 10 and conin exhibiting detail, this retina should have sists of two lei-metallic strips 42-43, each from 1,000 to 10,000 unitsyeach of which stri being formed of materials respectively would translate the variations in radiant of i h and low thermal ex ansion, the energy at its particular point in the image strips eing secured to a suitab e base 44 at into a variation in light and roduce an one end. Mounted between the free ends of imzigfi of variable light and dar s ots. the strips IS a small mirror 45, se-

en a very rough outline of t e object cured to the strips by fine wires 46. These a slight rotation of t e mirror. One of the strips is ex d to the'radiant energy and both are a ected equall "by changes in room temperature, so that t e mirror is moved only by the radiations. A. plurality of such units are assembled in close relation and 'light is reflected from the mirrors, and the dlfl'erent angular positions ofthe mirrors with respect to the source of li ht and the point of observation, produces a old of light and dark spots corresponding .to theimage 'in thermal radiation, thereby producing a visible image.

In Fig. 13 I have shown one form of observing system employing a plurality of thermal expansion units. A plurality of units, which are individually very small, are assembled in close relation on a panel filuand thermal radiation is concentrated on one of the strips 42, by the mirror 62. The panel is provided with apertures 63 throu h which a light beam is thrown onto the mlrrors 45 and the reflected beams from the mirrors normally pass through other apertures 64 in the panel. When the mirrors are deflected, the reflected beam will not pass through the aperture, and by observing all of the a er tures 64 the image may beobserved. he units are ve small and may be as small .as one-eighth 0 an inch in length and they are grouped closely, so that the apertures 64 are placed close together.

I claim:

1. The method of detecting the presence of a-body which consists in concentrating then mal radiation from the body on a thermosensitive body and translating the efiect of the radiation on said thermo-sensitive body into movement of a light ra 2. The method of detecting the presence of a body which consists in forming an image of the body in thermal radiation upon a thermo-sensitive body and translating the effect of the radiated image on said thermosensitive body into an image that may be observed by one of the senses.

3. The method of producing a visible image of a body in the dark which consists in forming an image of the body in thermal radiation on a thermo-sensitive body and translating the eii'ect of such image on said thermo-sensitive body into a visible image.

4. An apparatus of the character described, comprising a thermo-sensitive body movable 1n res onse to thermal radiation, means for pro ucmg an lmage in thermal radiation on said body, whereby movement is produced in the theme-sensitive body and nLelans for rendering said movement observa e.

5. An apparatus of the character described, comprising'a thermo-sensitive body movable in response to thermal radiation, a parabolic mirror arranged for, concentrating thermal radiation on said body whereby movement is (produced in said bod and nfians for ren ering said movement 0 serva e.

6. In an a paratus of the character described, a p urality of thermal expansion units, means for concentrating thermal radiation from a bod on a plurality of said units and means or observing the thermal ex ansion of said units.

In an apparatus of the character described, a plurality of thermal expansion units, means for concentrating thermal radiation from a body on a plurality of said units, a mirror attached to each unit and' adapted to be moved thereby, and means for observing the movement of the mirrors.

8. In an apparatus of the character described, a plurality of thermal expansion units, means for concentrating thermal radiation from a body on said units a mirror attached to each unit and adapted to be moved thereby, and means for throwing a light ray onto said mirrors whereby the movement of the mirrors may be observed,

9. In an apparatus of the character described,a plurality of thermo-sensitive units, means .for concentrating thermal radiation from a body on said units and a movable observable .element attached to each unit.

10. In an apparatus of the character described, a plura ity of thermo-sensitive units adapted to produce movement when subjected to temperature changes, means for concentrating thermal radiation from a body on said units and movable reflecting elements 

